Some prenatal tests are offered to all women as part of routine care in pregnancy. Other prenatal tests might be done because there is a greater chance that the baby could have a problem (eg physical or intellectual difficulties).

Prenatal testing is a choice and you may choose not to have any sort of testing.

Many parents are concerned that their baby will have some sort of birth defect. Although most babies will be healthy, about 1 in 40 babies (2.5%) are born with some problem. Some problems will be minor, but others may cause serious physical or intellectual difficulties.

Some problems can be found before birth, but not all.

Some prenatal tests are offered to all women as part of routine care in pregnancy. Other prenatal tests might be done because there is a greater chance that the baby could have a problem.

You may choose to have a test because you want to be reassured that your baby does not have the problem, or to prepare for a baby with problems, or to have the option of not continuing with the pregnancy.

Prenatal testing is a choice and you may choose not to have any sort of testing.

Before having a prenatal test you will have a chance to discuss the test with your doctor, midwife or a genetic counsellor. The type of tests that you choose will depend on advice from your doctor or midwife based on your medical, family and pregnancy history.

Some questions you might wish to ask are:

Which tests are best for me?

What will the test tell me about my baby?

How accurate is the test?

How and when is the test done?

What are the risks of having the test?

What are my options if the test shows my baby has a problem?

Your doctor or health care provider will support you whether or not you choose to have prenatal testing.

There are many things to consider before choosing whether or not to have a test in pregnancy. Other topics in this section of the site have information about specific tests during pregnancy. Always discuss any questions or concerns you have with your doctor.

Prenatal screening tests are tests that show if a baby has a higher chance of having a problem. Screening tests cannot tell for sure if a baby does or does not have a particular problem. All pregnant women, regardless of their age or family history, may choose to have one of these screening tests. It is not usual to have all the tests, as some look for the same problems.

In general screening tests pose no threat to the baby or woman. However test results that indicate a higher chance of having problems can cause anxiety and lead to the need to consider further tests, which may pose some risk to the baby.

Screening tests include

Nuchal translucency screening - an early ultrasound (for Down syndrome)

Prenatal diagnostic tests are tests that are able to tell, with a high level of accuracy whether or not a baby has a particular problem. These tests are offered to women who have a higher chance of having a baby with a problem.

Some of the tests have a small chance of causing a miscarriage. It is not usual to have all tests, as some of them look for the same problems.

No test can guarantee that your baby will be born healthy because prenatal tests can only detect some types of birth defects. The three main types of problems that can be detected in pregnancy are

Chromosomal abnormalities,

Some physical defects

Particular genetic conditions.

Chromosomal abnormalities

Any woman of any age can have a baby with a chromosomal abnormality. Although the chance of the baby having a chromosomal abnormality is small it does increase as women get older. Your doctor can give you information about your chances based on age.

Chromosomes are tiny structures contained in every cell of the body.

They contain the genetic information that controls how a baby grows and develops.

A baby inherits chromosomes from the parents' egg and sperm.

It is usual for a baby to receive 46 chromosomes in total.

Sometimes an error occurs before or soon after conception so that a baby receives too much or too little chromosomal material.

The most common example of this is Down syndrome, when a baby receives 47 chromosomes instead of the usual 46. People with Down syndrome usually have a characteristic facial appearance, varying degrees of intellectual disability and they may also have medical problems.

There are other types of chromosome abnormalities that are less common than Down syndrome. Some of them cause more serious problems than Down syndrome and others cause problems that are less serious.

Physical defects

A physical birth defect occurs when one or more parts of a baby do not develop normally. There are many types of physical birth defects, some are minor and some more serious. These include cleft lip and palate, a malformed heart, a limb with a part missing and spina bifida. Some, but not all physical birth defects may be detected by tests during pregnancy.

Genetic conditions

Genetic conditions are health problems that are caused when a person has an error in one of the genetic instructions (called genes). This may occur for the first time in a baby, or might be inherited from parents.

If you or your partner have a family history of a medical condition, or if you have previously had a baby with a genetic condition you may wish to know if it could occur in your baby. Prenatal testing may be available for the condition – and you should discuss this with your doctor before pregnancy. You may be referred to see a genetic specialist to get more information.

To help make decisions, have a look at the topic Genetic counselling on the Pregnancy, birth and baby site.